Other etching methods (MEMS Fabrication)

Other etching methods (MEMS Fabrication)

A wide variety of other etching techniques also exists, a few are listed below. All these methods can be used either singly or in combination to manufacture micro machines.

Bulk dry etching

In bulk dry etching, the liquid etchant is replaced by a gaseous plasma or ions. Plasma etchers and RIE (reactive ion etchers) are two examples of dry etchers. The etching takes place by chemical means, by physical bombardment of the silicon, or by some combination of both. A suitable mask which is resistant to etching must be chosen. By varying the gases in the etching chamber, both the etching characteristics and the mask selectivity can be changed. Dry etching advantages include high resolution (micron range) and wide variety of possible etching characteristics. Disadvantages include depths typically 25 microns or less (limited by masking material), loading effects (etch rate depends on amount of silicon 16 etched), and changing side wall profile.

Surface micro machining

Surface micro machining uses many masking layers to form thin structures on the surface of the wafer. Below each masking layer materials such as PSG (phosphosilicate glass) are used as sacrificial layers. After a masking layer has been patterned the underlying sacrificial layer may be removed. The resulting structures may be multi-layer and may be attached to the wafer or free to move. Surface micro machining has very high resolution (sub-micron is possible) but the output shapes are very thin (typically microns).

Laser micro machining

Laser micro machining uses a laser to locally change the etching environment. Dry or wet etching may be used. The increased local etching may be due to photo-chemistry, higher local temperature, or a combination of both. Alternatively, local deposition can be performed in place of local etching. Laser micro machining can produce very complex shapes but it is a serial rather than parallel process so only one part at a time may be machined. This increases the price per part and decreases the throughput.

LIGA

LIGA (a German acronym) uses an x-ray source to irradiate a radiation sensitive polymer. That polymer is then developed and a mold is formed. The mold is then used to make metal parts. The process is extremely accurate (sub-micron) and produces high aspect ratio structures (hundreds of microns deep) with vertical walls. Unfortunately, the required x-ray source makes LIGA very expensive, and limits the throughput.

Fuente: http://www.design.caltech.edu/Research/Publications/94h.pdf

Cesar Augusto Suarez
CI 17394384
CAF